Turbofan engines often include a reduction gearbox connecting the low pressure turbine shaft and the fan rotor, and one or more high speed booster rotor(s) between the fan reduction gearbox and the high pressure compressor. The booster rotor(s) are usually driven directly by the low pressure turbine shaft. Typically, two structural cases are provided in order to transfer the low pressure and high pressure loads to the engine mounts. Also, the presence of the booster rotor(s) between the fan reduction gearbox and the high pressure compressor usually requires the use of two separate oil bearing cavities for the fan gearbox and for the high pressure shaft bearings.